Despite an improved understanding about how influenza spreads within human and animal populations, the threat of global influenza pandemics remains high. This is because influenza viruses continue to evolve at an ever-increasing pace and because influenza vaccines fail to provide strong long lasting cross-protection against current isolates. Thus, there is an urgent need to explore innovative strategies to reduce transmission of influenza viruses between humans and animal species that serve as natural reservoirs for novel strains, such as swine. One possibility is to harness an immunoregulatory subset of T lymphocytes called natural killer T (NKT) cells that in mice induce protective immune responses that prevent or reduce influenza infections. This proposal seeks to identify how NKT cells respond to and may be targeted against influenza viruses for pigs and humans, because of the importance of this pathogen for commercial pork producers and to prevent the transmission of influenza viruses from pigs to people. Pigs also provide an excellent model to understand how human NKT cells might respond to and be targeted against influenza infections. Thus, the current application seeks support for the dual purpose of harnessing NKT cells to protect both humans and swine from influenza through three overlapping aims. In Specific Aim 1 we will explore whether NKT cells help protect pigs from influenza virus infections. We will determine if CD1d-knockout swine that lack NKT cells are more susceptible to influenza infection compared to CD1d-intact pigs that are NKT cell sufficient. This aim will provide valuable insight into whether NKT cells help protect humans from influenza infections, because pig and human NKT cells are phenotypically very similar. Specific Aim 2 will establish the parameters whereby therapeutic activation of NKT cells improves the efficacy of SI virus vaccines. We have already shown that NKT cell agonists induce profound adjuvant effects that boost vaccine-mediated immunity against homologous challenge. In Aim 2 we will extend these findings to determine whether NKT cell agonists can enhance killed or modified live virus vaccines to provide cross-protection against heterologous and heterosubtypic virus strains. Finally, Specific Aim 3 will determine if the antiviral effects of NKT cell agonists can be used to reduce the severity and transmissibility of established influenza infections to improve the course of disease in pigs and humans. These independent but interconnected aims offer the opportunity to better understand NKT cell function in the context of an influenza virus infection in a natural host species; this knowledge can be utilized in both humans and swine to limit the current cycle of swine-to-human transmission of influenza viruses. Our objectives strongly align with the mission of this funding opportunity: to utilize an agriculturally important domestic animal species to improve human health through the advancement of basic and translational research deemed highly relevant to both agricultural and biomedical research.